The activity of cellulase is one in which cellulosic fibres or substrates are attacked by the cellulase and depending on the particular function of the cellulase, which can be endo-or exo cellulase and the respective hemicellulases. The cellulose structures are depolymerized or cleaved into smaller and thereby more soluble or dispersible fractures. This activity in particular on fabrics provides a cleaning, rejuvenation, softening and generally improved handfeel characteristics to the structure. This has been previously speculated to be cleavage of fibrils from the surface of fibres such that the main strand of the fibre becomes smoother, less available for incrustations, less likely to entangle with other fibers and optically less defuse in its light reflecting and emission.
Naturally, improvements in the activity of particular cellulase compositions have been made over time in order to allow lower usage or shorter exposure times for similar benefits. In the detergent field cellulases performing in a typical detergent wash environment are available with an activity at which the desired cellulase performance is reached prior to the end of a wash-cycle. However, since the cellulase continues to react, even after having provided the desired performance, cleavage of the cellulose will continue. Therefore, there is a potential risk of tensile strength loss. It should be noted however, tensile strength loss of fabric is also an unavoidable result of mechanical action due to use/wearing and may further result from damage by a bleaching component in the laundry process, especially if the fabric is contaminated with metal compounds.
The obvious solution to the above problem is to use the appropriate amount of cellulase such that the time of a wash-cycle is coinciding with the required time for the desired cellulase performance while tensile strength loss is not yet occuring in a significant amount. This however has proven difficult due to varying wash-cycles depending on local custom, washing machine equipment, cloths and soiling of the cloths be washed, additional additives incorporated into the detergents for other unrelated reasons and degradation of the cellulase upon storage. Therefore a better way to provide the cellulase benefit while preventing fabric damage, is desirable.
According to the present invention, this is provided by including such an amount of cellulase that the desired cellulase activity is certainly achieved prior to the end of the wash-cycle while a cellulase terminator provides the means to prevent potential tensile strength loss within that time.
Cellulase exhibiting exceptionally high activity have been disclosed in the context of compact detergents in WO-92-13057, in the context of quaternary ammonium softening compounds in EP-A-495 554 and in the context of softening clay in a detergent composition in EP-A-495 258 and EP-A-177 165. Cellulase as such with exceptionally high activity has been disclosed in WO 91/17243. Recognition of the potential tensile strength loss of cellulase has been reported in several publications. For example Japanese application J-62-310754 discloses particular cellulases having a specific so-called non-degrading index. Japanese application J-63-134830 discloses detergent compositions for clothing containing a cellulase which has a non-destructive index and U.S. Pat. No. 4,978,470 discloses a detergent composition for closing containing cellulase enzyme with a "non-degrading index" of less than 500.
The attempt to fine tune the cellulase activity to eliminate the problem underlying the present invention as discussed above has its appeal more in the field of industrial cleaning where defined conditions in particular length of fabric exposure to the cellulase, can be assumed. For the typical household conditions, the variation of individual situations encountered, are so multiple that a high activity cellulase together with a terminator is a substantially better approach to ensure the desired cellulase activity thereby preventing potential tensile strength loss of the fabrics.